Mass RCS adoption is a goal for both Google and Samsung, and both companies have publicly stated that Google Messages is the vehicle for achieving this.
Most carriers are transitioning to Google's version of RCS because it runs through Google's servers, tends to be more compatible with iOS, and doesn't require the carrier to build and maintain their own RCS infrastructure.
While they aren't exactly the same, you can think of Google Messages as the Android equivalent to iMessage. Apple is able to offer advanced messaging features by running iMessage through their private servers. Google is doing the same with Google Messages and RCS.
You can still use other texting apps if you want, you just arent going to have access to RCS.
